1. Field of the Invention
The present invention relates to an automatic focusing control using a contrast of an object.
2. Description of the Related Art
Image capturing apparatuses such as digital still cameras and digital video cameras widely use a contrast AF system for performing automatic focusing based on contrast evaluation values that are obtained by bandpass filtering image signals horizontally read out from an image sensor. In recent years, techniques that calculate a vertical contrast evaluation value in addition to a horizontal contrast evaluation value and perform automatic focusing based on both the horizontal and vertical contrast evaluation values have also appeared. Meanwhile, advances in face detection and face recognition techniques has resulted in the wide application of techniques that identify a person's face region from a captured image and perform automatic focusing using the face as a focus measuring frame.
For example, Japanese Patent Laid-Open No. 2008-139683 describes a technique that computes both horizontal and vertical contrast evaluation values with respect to a focus measuring frame set on the face region and weights the vertical contrast evaluation value. Also, Japanese Patent Laid-Open No. 2004-317699 describes a technique that sets a frame only on the eye region in the case where a face that is larger than a predetermined size is detected.
However, with Japanese Patent Laid-Open No. 2008-139683, a considerable amount of line memory needs to be secured for acquiring vertical contrast components in the case where the size of the detected face is large, since a focus measuring frame that matches the size of the face needs to be provided. Also, with Japanese Patent Laid-Open No. 2004-317699, the fact that only the component of the eye region is extracted out of the vertical contrast components included in the face leads to concern about deterioration of the S/N ratio when focus adjustment is performed, due to not being able to effectively utilize the biological characteristic of there being lots of contrast components in the vertical direction of the face.